Question

what kind of combustion is observed in alkanes why do air holes of a gas burner have to be adjusted when vessel being heated gets blackened
by the flame

Answer 1

Alkanes undergo complete combustion in sufficient supply of oxygen and burns with blue flame with no smoke.
In limited supply of oxygen alkanes undergo incomplete combustion with a yellow sooty flame and leaves a black residue.
Air holes have to be adjusted when vessel being heated gets blackened by the flame so sufficient apply of air reaches and complete combustion takes place and there is no blockage in air pathway.

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